Ok, try

#!perl
use strict;
use Time::Piece;
my @CommonLogFiles = qw( log1.txt log2.txt);

my $re = qr[TIMESTAMP=... (... +\d{1,2} \d\d:\d\d:\d\d 20\d\d)];

my @records = ();

for my $log (@CommonLogFiles) {
  open LOG, '<', $log or die "Could not open $log: $!\n";
  print "Just opened $log...\n";
  my $record;
  my $datetime;
  while (<LOG>){
    # start of record
    if (/^<\d+>/){
      $record = "[$log] ".$_;
      next;
    } else {
      $record .= $_;
    }
    
    # extract datetime
    if (/$re/){
      $datetime = Time::Piece->strptime($1,'%b %d %T %Y')->datetime;
      #print "$1 => $datetime\n"
    }
    
    # save record with datetime
    if (/END OF REPORT/){
      $record .= "\n";
      if ($record =~ /MSGCLS/m){
        push @records,[$record,$datetime];
        $record = '';
      }
    } 
  }
  close LOG;
};

# Schwartzian_transform
my @sorted = map { $_->[0] }      
             sort { $a->[1] cmp $b->[1] } @records;

open SORTED,'>','sorted.log' or die "$!";
print SORTED $_ for @sorted;
close SORTED;
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